Children who spent more than two hours a day on "screen time" over the two years were at increased risk, as were those with low levels of physical activity.

This study supports previous evidence that a sedentary lifestyle and low levels of physical activity are associated with high blood pressure, although it does not prove that the former causes the latter.

There are many factors that can affect blood pressure, including genetics, development in the womb, socioeconomic status and weight.

That said, the more time your child spends watching TV or playing on their PlayStation 4, the less time they are physically active.

Where did the story come from?

The study was carried out by researchers from several academic centres worldwide, including the University of Glasgow in the UK. It was funded by the European Community Sixth Research, Technological Development and Demonstration Framework Programme.

The study was published in the peer-reviewed medical journal International Journal of Cardiology.

Both The Daily Telegraph's and the Daily Mail's reporting was fair, although neither paper included comment from independent experts, and they failed to explain the fact that this kind of study cannot prove cause and effect.

What kind of research was this?

This was an observational cohort study looking at the incidence of pre-high blood pressure and high blood pressure in children in Europe and any association between blood pressure, levels of physical activity and sedentary behaviour.

The study's authors say high blood pressure is one of the most important factors for cardiovascular disease, and studies have shown that blood pressure levels in children and adolescents are linked to high blood pressure in adulthood. However, little is known about the risk factors for high blood pressure in childhood. Their hypothesis is that low levels of physical activity (and high levels of sedentary behaviour may contribute to the development of high blood pressure.

Sedentary behaviour was classified as the amount of time parents reported their children spending in front of a screen - whether watching TV, videos or playing computer games. It did not include other kinds of sedentary activity - such as reading.

Blood pressure is measured in millimetres of mercury (mmHg) and is recorded as two figures:

systolic pressure - the pressure of the blood when your heart beats to pump blood out

diastolic pressure - the pressure of the blood when your heart rests in between beats, which reflects how strongly your arteries are resisting blood flow

In children, high blood pressure is defined as blood pressure greater than the 95th percentile for their age, height and gender.

What did the research involve?

The researchers used data from a study of 16,224 children from eight European countries (Spain, Germany, Hungary, Italy, Cyprus, Estonia, Sweden and Belgium) looking at the effects of diet and lifestyle on health. The current analysis was based on 5,221 children who were between two and 10 years old at the start of the study, for whom all data was available. Of these, 5,061 children were re-examined two years later.

The children had their systolic and diastolic blood pressure measured at the start of the study and at two years follow-up. Pre-high blood pressure was defined as systolic or diastolic blood pressure from the 90th to 95th percentile for their age and height; and high blood pressure was defined as systolic or diastolic blood pressure above the 95th percentile for age and height.

Physical activity in the children was measured using an accelerometer - an electronic device which measures the intensity of exercise. The unit had to be worn for at least six hours a day, for at least three days during one week (two weekdays and one weekend day).

From this, the researchers calculated the time children spent in moderate physical activity and in vigorous physical activity. Moderate activity includes activities such as cycling, while vigorous activity includes running, football and energetic dancing.

The children were classified into two groups - those who met current physical activity guidelines - doing at least 60 minutes of physical activity daily - and those who did not meet the guidelines. They were further classified as to whether changes in physical activity levels had taken place over the two years.

The children's parents were asked to fill in a questionnaire on their children's sedentary behaviour, as measured by hours of TV/DVD/video viewing and computer/games-console use for both typical weekdays and weekend days. Researchers used this information to calculate the children's "total screen time" per day. Participants were classified into two groups - those who met (US) guidelines on total screen time (two hours or less a day) and those who did not. Researchers also calculated changes in sedentary behaviour at two years.

They also included a range of potential confounders, including season, sex, age, parental education and waist circumference.

Researchers estimated the relationship between physical activity levels, reported screen time and the risk of developing high blood pressure or pre-high blood pressure.

What were the basic results?

Researchers found that the yearly incidence of pre-high blood pressure was 121 per 1,000 children, and high blood pressure was 110 per 1,000 children.

Children who maintained sedentary behaviour of more than two hours a day during the two year follow-up had a 28% higher risk of having high blood pressure (relative risk (RR) 1.28, 95% confidence interval (CI) 1.03 to 1.60).

Children not performing the recommended amount of physical activity (60 minutes a day) at the start of the study had a 53% higher risk of high blood pressure (RR 1.53, 95% CI 1.12 to 2.09).

There was no association between pre- high blood pressure and children's behaviours.

How did the researchers interpret the results?

The researchers say that the incidence of pre-high blood pressure and high blood pressure is high in European children, with those doing less than 60 minutes of physical activity daily or spending two hours or more per day in front of a screen at higher risk. They say that the results suggest regular physical activity should be promoted and sedentary behaviour discouraged in children to prevent high blood pressure and its consequences in adulthood.

Conclusion

The study found a worryingly high incidence of high blood pressure in children of just over 10%, instead of the expected 5%. It also found that low levels of physical activity and high levels of "screen time" raised the risk.

Although researchers adjusted their analysis for a range of other factors which might affect blood pressure (called confounders), it is always possible that other unmeasured factors could have affected the results. In addition, the study was reliant on parental estimates of the amount of sedentary behaviour their children had per day, which may be an over- or underestimate. Wearing the accelerometer may also have influenced the amount of physical activity that was performed on those days, which could also affect the results.

It's generally agreed that many of today's children spend too much time in front of a screen - and too little on physical activity. The real question is - what can we do about it?

Children are more likely to accept changes to their lifestyle if they involve the whole family. Read more about getting healthy as a family.

Also, evidence has shown that placing limits on the use of any type of screen equipment in the hours before bedtime can improve the quality of their sleep. This could then help them improve their energy and activity levels during the day.

Summary

"Watching TV for more than two hours a day increases the risk of raised blood pressure in children," The Daily Telegraph reports. A large study, involving more than 5,000 children who were followed up over two years.